wmd text editor executes the code

Question

I am using WMD text-editor in my website as

 <link rel="stylesheet" type="text/css" href="wmd-master/wmd.css" />
  <script type="text/javascript" src="wmd-master/showdown.js"></script>
  <link rel="stylesheet" href="styles/index2.css">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css">

But whenever I put a code in WMD editor, the code gets executed. How can I stop this?

for example:

It can be seen in the demo of WMD editor as well. WMD DEMO Thanks in advance.